Strength Capabilities While Performing Torquing Tasks in Weightlessness

Abstract

Knowledge of individuals' strength capabilities in weightlessness is of interest within many areas of NASA, including workplace design, tool development, and mission planning. This study was a generic examination of the loads produced by individuals performing maximal efforts with a torquing tool in zero-gravity. The study also examined the effects of orientation and direction of rotation of the tool on strength effectiveness. An experiment was conducted aboard NASA's reduced gravity aircraft which simulates brief periods of weightlessness. A test stand was developed and instrumented to measure the loads applied to fixed fittings. Eight male volunteers participated in this study in which they used a wrench to apply a maximum torque to fittings oriented along each of three orthogonal axes. It was seen that these subjects could produce approximately 400 to 750 N of force, depending on the orientation of the tool and the direction of effort. The most force could be produced when pushing the tool upwards. A force effectiveness ratio (FER) was defined as an indication of how much of the subject's total effort actually went into performing the desired task. Values of FER ranged from 0.55 to 0.90, with the greatest FER occurring with UP and DOWN efforts, and the lowest with AWAY and LEFT efforts. Designers can use these results to set specifications for craft structures; tools can be developed based on the known strength of the tool users; and tasks can be developed to not exceed the crewmembers' capabilities.